1. Field of the Invention
The present invention relates to an improved process and apparatus for eliminating non-condensible gas from a halocarbon vapor compression refrigeration system. More specifically, the invention relates to further processing of a vapor stream from over the liquid refrigerant exiting the condenser on the high pressure side of the expansion valve by use of a second compression cycle and semipermeable membrane separation step.
2. Description of the Prior Art
Halocarbon vapor compression refrigeration systems have become necessary and an integral part of modern life. Household refrigerators and freezers, home air conditioners, heat pumps, automobile air conditioners, industrial air conditioners, industrial freezers, as well as in cooling of brine and water in industrial processing all use halocarbon vapor compression refrigeration systems. Such systems use refrigerant fluids such as monochlorotrifluoromethane, trichloromonofluoromethane, dichlorodifluoromethane, monochlorodifluoromethane, trichlorotrifluoroethane, tetrafluoroethane, monochloropentafluoroethane, and mixtures such as those of monochlorodifluoromethane, and monochloropentafluoroethane, and of dichlorodifluoromethane and difluoroethane as circulating refrigerant fluid in a system comprising a compressor, a condenser, a fluid expansion means, and an evaporator. The working fluids are therefore low boiling liquids boiling in the range from about -90.degree. C. to about 50.degree. C. In operation, the circulating fluid is first compressed and then cooled in the condenser, liquifying the fluid and the liquid is then allowed to vaporize in the evaporator thus cooling the environment of the evaporator.
For most domestic applications, the halocarbon vapor refrigeration systems such as refrigerators, freezers, room air conditioners, and the like are systems hermetically sealed at the factory; i.e., sealed systems wherein after evacuation of the system and the refrigerant charge is introduced into the system the whole system is permanently sealed by soldering or brazing. For the most part the evacuation and the sealing of the systems for domestic use are done carefully such that most of the household refrigeration systems are trouble-free for many years.
However in most industrial applications of the refrigeration systems, the evaporation unit, compressor unit, and condenser unit are usually spaced away from each other and therefore the evacuation of the system, the charging of the refrigerant, and the sealing of the system are usually carried out under less than ideal conditions at the location of the industrial system. Under such conditions, less than adequate evacuation and faulty sealing may permit presence of non-condensible air in the refrigeration system. The presence of non-condensible material in the recycling refrigerant composition lowers the efficiency of the refrigeration system and when the non-condensibles are present in sufficient amounts may lead to the failure of the compressor. Aside from the initial occlusion of air in the recirculating refrigerant composition, any leak, particularly in the evaporator and/or low pressure side of the compressor where sub-atmospheric pressure frequently exists during normal operation, will add air to the system. Even when no air is present initially, non-condensible gas may originate from the thermal decomposition of the refrigerant itself as well as from the thermal decomposition of lubricants and stabilizers present in the refrigerant compositions. These thermal decompositions are more likely to occur in a large scale industrial application than in a smaller domestic units due to the considerably more severe operating environment of the industrial units.
In view of these known problems associated with the accumulation of contaminant gases in a vapor compression refrigerant system, certain proposed modifications to the conventional refrigeration cycle have recently been proposed. For example. U.S. Pat. No. 4,316,364 uses an elongated vertical gas accumulating chamber positioned in the high pressure side of the refrigerant circuit along with a temperature indicator to trap non-condensible contaminant gases and measure their temperature. A depressed temperature relative to the temperature of the condensed refrigerant is used as an in-situ indication of the onset of a malfunction. Similarly, in U.S. Pat. No. 4,417,451 the inlet to the elongated vertical gas accumulator chamber is equipped with a perm-selective membrane and a purge valve is used to exhaust unwanted contaminant gases accumulated therein.